The compression hip screw (also referred to as a dynamic hip screw or sliding hip screw) is a commonly used fracture fixation device for femoral neck and intertrochanteric fractures of the proximal femur. A variety of similar devices are available from multiple orthopaedic device manufacturers. A generic compression (dynamic, sliding) hip screw (FIG. 1) consists of three basic components: a lag screw which is screwed into the femoral head to secure the proximal fracture fragment; a side plate containing a hollow cylindrical portion for sliding interdigitation with the lag screw and an integrally attached bone plate for screw fixation to the femoral diaphysis; and a compressing screw which may be threaded into the lateral end of the lag screw and tightened against the side plate to draw the lag screw laterally within the cylindrical portion of the side plate.
The utility of the compression hip screw for fixation of the most common femoral neck and intertrochanteric hip fractures, with fracture planes relatively perpendicular to the anatomical axis of the femoral neck (and of the corresponding axis of insertion of the lag screw portion of the compression hip screw fixation device), is well documented. The ability of the lag screw portion of the fixation device to slide within the mating cylindrical portion of the fixation device side plate allows the fracture site to compress into a stable configuration when weight is applied to the femoral head or, alternatively, when the compressing screw is tightened. When tightened, the compressing screw pulls the lag screw (and attached proximal fracture fragment) laterally and, in the process, compresses the proximal (medial) and distal (lateral) fracture fragments. This is desirable, as a forcefully compressed interdigitation of irregular fracture fragments produces a stable fixation configuration.
The utility of the generic compression hip screw falls short when the fracture plane is relatively parallel to the femoral neck and corresponding axis of insertion of the lag screw portion of the fixation device. This fracture configuration is commonly referred to as a “reverse obliquity fracture.” If the prototypical hip screw is used for fixation of a reverse obliquity facture, loss of reduction with lateral displacement of the proximal fragment is a frequent sequela. The forces of bearing weight, or even resting muscle tone, produce a shear force along the plane of the reverse obliquity fracture causing the proximal fracture fragment(s) to shift laterally relative to the distal diaphysial fragment. There is no design feature in the typical compression hip screw to stop this translation. In fact, the entire purpose of the compression hip screw, as currently configured, is to allow sliding translation.
Current recommendations for fixation of reverse obliquity fractures include low angle fixed blade plates, intramedulary fixation devices and external fixation hardware. Although each of these methods has its advocates, the relative ease and familiarity of use of the generic compression hip screw leads many orthopaedic surgeons to select this fixation methodology, where other choices may be more appropriate from a biomechanical perspective. This, and other factors related to alternative fixation methodology complications (Shaw et al.), lead Cole and Bhandari to decry, in a recently published update on orthopaedic trauma (Cole et al.), “ . . . what is blatantly missing from contemporary locking plate inventories: an effective locking fixator for the proximal femur.”
The optional locking capacity of the described Locking Compression Hip Screw extends the spectrum of fixation capabilities of the generic compression hip screw. When locked, the lag screw cannot slide within the mating side plate and, hence, will block lateral translation of the proximal fracture fragment, which is securely anchored to the lag screw via the large cancerous bone threads on its medial aspect. Once the hardware is locked, the reverse obliquity fracture (or high subtrochanteric fracture) can be compressed by releasing limb traction, attaching a routine compressing apparatus to the femur and side plate and/or utilizing the compression capability of the offset screw holes built into the side plates of most compression hip screw systems.